Malcolm Myatt, 68, had a stroke. It affected the frontal lobe of his brain--the part of the brain that governs emotions. As a result, he's lost the ability to be sad:

Experts have confirmed that it is not uncommon for strokes to cause psychological, emotional and behavioural changes.

The retired lorry driver said: "I am never depressed. Being sad wouldn't help anything anyway. I would definitely rather be happy all the time than the other way round. It's an advantage really.

"The stroke could have become my worst enemy but I wouldn't let it. Now I barely even notice that I don't feel sadness.” [...]

Many of the psychological changes that occur after a stroke are down to the physical damage of the brain, and will depend upon which part of the brain has been affected and the extent of the damage, The Stroke Association said.

Dr Clare Walton explained: “When a stroke strikes, the blood supply to the brain is cut off, brain cells die and permanent damage can be caused. Every stroke is different, and the area of the brain that’s damaged will determine how the person is affected.